A high-power green picosecond laser based on the ‘Z-slab’ Nd:YAG amplifier is presented. The edge-pumped zigzag amplifier was designed to achieve high energy scaling with good beam quality. In a master oscillator power amplifier system 120 W average power was produced at 1064 nm, which was frequency doubled to 84 W at 532 nm. The maximum pulse energy was 400 μJ at 1064 nm and 280 μJ at 532 nm. The repetition rate was variable from 250 to 1000 kHz with M2 < 1.4. In burst mode with 1-10 pulses, over one millijoule total burst energy was demonstrated at 1064 nm.